Enhancements in Java 增强特性
Enhancements in Java 增强特性，Java Language Changes for Java SE 9，分别介绍了Java 5至Java 9的增强特性，这里继续介绍后续版本的新特性。
JDK 10：移除了javah
- 286：Local-Variable Type Inference，本地变量类型推断
var list = new ArrayList<String>(); // infers ArrayList<String>
var stream = list.stream(); // infers Stream<String>
JDK11：2018/09/25，移除了javaee和corba，支持TLS 1.3，废弃Nashorn和Pack200
- 321：Http Client，http客户端，intro
HttpClient client = HttpClient.newHttpClient();
HttpRequest request = HttpRequest.newBuilder()
.uri(URI.create(http://openjdk.java.net/))
.timeout(Duration.ofMinutes(1))
.header("Content-Type", "application/json")
.POST(BodyPublishers.ofFile(Paths.get("file.json")))
.build();
HttpResponse<String> response = client.send(request, BodyHandlers.ofString());
client.sendAsync(request, BodyHandlers.ofString())
.thenApply(response -> { System.out.println(response.statusCode()); return response; } )
.thenApply(HttpResponse::body)
.thenAccept(System.out::println);
//BodyPublishers::ofByteArray(byte[]) ofString(String) ofInputStream(Supplier<InputStream>)
//BodyHandlers::ofByteArray() ofFile(Path) discarding() - 323：Local-Variable Syntax for Lambda Parameters
(var x, var y) -> x.process(y) - 330：Launch Single-File Source-Code Programs，执行单源码文件
java HelloWorld.java
- 325：Switch Expressions (Preview)，多条语句时使用花括号和break
int numLetters = switch (day) {
case MONDAY, FRIDAY, SUNDAY -> 6;
case TUESDAY -> 7;
case THURSDAY, SATURDAY -> 8;
case WEDNESDAY -> { break 9; }
};
- 354：Switch Expressions (Second Preview)，使用yield（替代break）返回值
int i = switch(day){
default –> yield 0;
} - 355：Text Blocks (Preview)，文本块适用于html、sql、javascript等
String html = """
<html>
<body>
<p>Hello, world</p>
</body>
</html>
""";
String query = """
SELECT `EMP_ID`, `LAST_NAME` FROM `EMPLOYEE_TB`
WHERE `CITY` = 'INDIANAPOLIS'
ORDER BY `EMP_ID`, `LAST_NAME`;
""";
ScriptEngine engine = new ScriptEngineManager().getEngineByName("js");
Object obj = engine.eval("""
function hello() {
print('"Hello, world"');
}
hello();
""");
JDK14：2020/03/17，新增jpackage，转正switch，移除Pack200，
- 305：Pattern Matching for instanceof (Preview)，类型判断并声明变量
if (obj instanceof String s && s.length() > 5) {
// can use s here s.contains(..)
} else {
// can't use s here
}
@Override public boolean equals(Object o) {
return (o instanceof CaseInsensitiveString cis) &&
cis.s.equalsIgnoreCase(s);
} - 358：Helpful NullPointerExceptions
a.i = 99; //a为null时错误信息更加详细
Exception in thread "main" java.lang.NullPointerException:
Cannot assign field "i" because "a" is null
at Prog.main(Prog.java:5) - 359：Records (Preview)，替代lombok，自动提供方法getter constructor equals hashCode toString，不可变更对象
record Point(int x, int y) { }
boolean Class#isRecord() - 370：Foreign-Memory Access API (Incubator)，堆外内存访问
VarHandle intHandle = MemoryHandles.varHandle(int.class,
ByteOrder.nativeOrder());
VarHandle intElemHandle = MemoryHandles.withStride(intHandle, 4);
try (MemorySegment segment = MemorySegment.allocateNative(100)) {
MemoryAddress base = segment.baseAddress();
for (int i = 0; i < 25; i++) {
intElemHandle.set(base, (long) i, i);
}
}
JDK15：移除Nashorn，改进DatagramSocket，
- 338：Vector API (Incubator)
